Yes, there are likely 'Bardock Kills Frieza' fanfics out there. The Dragon Ball universe has a huge fan base, and many fans like to create alternative storylines. You can try searching on fanfic websites like FanFiction.net or Archive of Our Own.
The plot could start with Bardock having a premonition of Frieza's future actions against the Saiyans even before the destruction of Planet Vegeta. He then secretly trains and discovers a new form or power that allows him to stand up to Frieza. When Frieza arrives to destroy the Saiyans, Bardock reveals his newfound strength and battles Frieza. After a long and intense fight, Bardock manages to defeat and kill Frieza, changing the course of the Dragon Ball universe. This could also lead to new alliances and power struggles among the remaining characters.
Well, it could be that in the fanfic, Bardock's group forms an unexpected alliance. Perhaps they team up with another powerful race or a group that has some sort of technology or magic that can counter Frieza. This alliance provides them with the means to not only fend off Frieza but also to ensure their survival. Another possibility is that there is some sort of time - travel or dimension - hopping involved. They could escape to a different time or dimension where Frieza can't reach them.
In a 'Bardock's group survive Frieza' fanfic, a major element is the alteration of the power balance. This can be achieved in multiple ways. For example, the fanfic might introduce a powerful artifact that boosts the Saiyans' power. The relationships within Bardock's group are also important. If they have strong bonds and are able to communicate effectively, they can better coordinate against Frieza. Moreover, the fanfic may explore different Saiyan cultural elements that give the group an edge. For instance, a long - forgotten Saiyan ritual or knowledge that helps them in their fight for survival.
A 'bardock vs king vegeta fanfic' could explore the backstories of both characters. Bardock's story as a Saiyan who starts to question the Frieza regime might contrast with King Vegeta's more traditional and perhaps self - serving rule. Their fight could be a symbol of the changing tides within the Saiyan community. It could also introduce new elements to the Dragon Ball lore, like different forms of Saiyan power that are unique to this fictional encounter.
A plotline could start with Frieza hearing about Broly's power and being jealous. He then devises a plan to ambush Broly. But Broly, being extremely perceptive in his own way, senses Frieza's approach and is ready for the fight. As the fight progresses, Frieza realizes that Broly is much stronger than he expected and has to use all his dirty tricks to try and win. Or perhaps the plotline could involve Broly being captured by Frieza's forces, and then Broly breaks free and goes on a rampage against Frieza and his minions.
One of the main themes is the clash of generations. Goten represents the new generation of Saiyans while Frieza is from an older, more menacing era. This creates an interesting dynamic. Survival is also often a theme, as Goten has to fight to survive against Frieza's brutal attacks. Additionally, the theme of justice can be seen, where Goten is fighting for what he believes is right against Frieza's tyranny.
Another theme could be loyalty. Bardock might be loyal to the true potential of the Saiyan race while King Vegeta is loyal to the existing power structure. This difference in loyalty can create a great conflict in the fanfic. Also, there could be a theme of social change. As Bardock may represent the underclass Saiyans who want a change, and King Vegeta is the symbol of the old regime.
A possible fanfiction could focus on a group of Saiyans who are trapped in a dimension where they can only watch the Goku vs Frieza fight on repeat. They start to notice small details in the fight that they hadn't before, like the exact moment Goku's power level spikes or how Frieza is trying to adapt his strategy. This newfound knowledge could then be used by them in some way when they eventually break free from that dimension.
Trunks would also be interested. He has his own experiences with fighting powerful foes and would be eager to see how Goku, a great Saiyan warrior, fares against Frieza. Also, the younger Saiyans like Goten might be interested. They've heard stories about Frieza and would be excited to see their father or other Saiyan heroes in action against such a notorious villain.